CD27 CD70 INTERACTION DIRECTLY DRIVES B-CELL IGG AND IGM SYNTHESIS/

CD27 is a T cell activation antigen expressed on a majority of periphe ral blood T cells. CD27 is also expressed on a subpopulation of human B cells, and it is reported that CD27(+) B cells secrete both IgG and IgM. CD70, a ligand for CD27, is expressed on activated T and B cells, suggesting an interaction between T and B cells via CD27/CD70 ligatio n. Here, we analyze B cell immunoglobulin synthesis using a CD70 trans fectant and present functional data showing that B cells secrete large amounts of IgG and IgM as a result of the CD27/CD70 interaction. A fl ow cytometric analysis showed that CD27 expression was increased and C D70 was expressed on tonsillar and peripheral blood B cells after acti vation with Staphylococcus aureus Cowan strain (SAC) plus interleukin (IL-2). In addition, the proliferation of B cells was enhanced mildly by the addition of CD70 transfectant, and its proliferation was blocke d by anti-CD70 mAb. More importantly, the CD70 transfectant enhanced I gG and IgM production by purified B cells greatly in the presence of S AC plus IL-2. The enhancement was completely blocked by the addition o f either anti-CD70 mAb or anti-CD27 mAb. Strongly suggesting that the interaction of CD27 with its ligand, CD70, on B cells plays an importa nt role in B cell growth and differentiation to produce IgG and IgM.